Removal of solder from a substrate or component is a necessary process that is widely practiced for the repair or rework of electronic assemblies. Electronic components, whether of the surface mount or pin through hole type are usually joined to a supporting substrate with solder joints between individual tabs or pins on the component and corresponding surface pads or holes surrounded by pads on the substrate. When a component or chip is removed from a substrate due to some known or suspected defect in the component or attachment, an excess of solder of random or irregular shape often having a rough surface is left behind on the substrate component attachment pads. Such surfaces are unsuitable for attaching another component or re-attaching the same component without first removing the excess solder to provide a uniform surface on the attachment pads. Components including semiconductor chips may also have excess solder which needs to be removed prior to use or re-use.
Various methods have been developed for removing solder from a substrate or component. For example, vacuum suction has been used to achieve solder removal using apparatus such as disclosed in U.S. Pat. No. 3,970,234. Use of vacuum suction apparatus is undesirable because it is complicated to make and use, and the results are highly de pendent on operator skill. Furthermore, due to clogging with solder, vacuum suction tips can not be made smaller than about 10 mili-inches in diameter, preventing their use on chip sites and other fine pitch arrays of solder pads.
Another method for solder removal involves apparatus to heat the solder above its melting point and then using a wick to draw the molten solder from the surface of the substrate or component.
Accordingly, a great variety of wicks have been developed. For example, strands of copper coated with solder and braided together to form a wick are disclosed in U.S. Pat. No. 4,164,606 while U.S. Pat. No. 4,416,408 describes a wick made from an open mesh of strands. A wick made of a non-metallic material coated with metal and flux is disclosed in U.S. Pat. No. 4,323,631.
A wick formed by etching a pattern in a silicon base and then metallizing the pattern is described in U.S. Pat. No. 5,065,931. Japanese Patent No. 1-192466 uses a printed circuit board having holes which absorb melted solder by a capillary phenomenon into the holes. Browne and DiNunzio describe using a copper block with cone shaped aligned protrusions to wick solder up into the copper block in IBM Technical Disclosure Bulletin Vol. 27, No. 5, May 1994 p. 35. Caccoma et. al. describe a solder wick ribbon apparatus for solder removal in IBM Technical Disclosure Bulletin Vol. 21, No. 11, April 1979, p. 4482.
Porus metal blocks have also been used for absorbing solder. Methods for making such devices are described in IBM Technical Disclosure Bulletin Vol. 25, No. 5, October 1982, p. 2285 and in U.S. Pat. No. 5,219,520. Once a block becomes filled with solder it must be replaced, making this approach undesirable because the blocks are expensive to manufacture.
Solder material has also been removed by using a jet of hot oil as described in IBM Technical Disclosure Bulletin, Vol. 12, No. 4, September 1968, p. 548 or a stream of hot gas to dislodge excess solder making it part of the jet stream as disclosed in IBM Technical Disclosure Bulletin, Vol. 18, No. 5, October 1975, P. 1384-85. Fluid impingement methods such as these can result in solder residue becoming embedded in the substrate surface due to the high velocity of the stream.
The substrate can be partially or completely immersed in a liquid bath of solder as in IBM Technical Disclosure Bulletin, Vol. 19, No. 7, December 1976, p. 2476 or another fluid as in U.S. Pat. No. 5,620,132. With immersion, solder removal can be enhanced by passing a squeegee over the surface of the substrate after the solder has become melted, or by using an adhesive material to pull the solder away from the substrate after it is raised to its melting point as in U.S. Pat. No. 5,458,281. Immersion methods necessarily require apparatus for containing and heating the fluid and means for removing solder from the container as it accumulates or else periodically replacing the fluid.